Personally, I think that a large pit, preferably one with a ravenous beast as a permanent resident, would be the perfect idea for the center of the area. This would have a significant effect on several important problems.
1) It would lessen crowds in the area as many people would fall into the pit.
2) The people that fall into the pit would most likely be of the type that don't look where they are going. This would, in effect, reduce the problem of mindless people bumping into others all over both parks.
3) People would no longer sit in the area at night to view the fireworks creating a serious hazard for those trying to get from DCA to DL.
4) This would create a much needed entertainment venue ala Rome's Colosseum as entertainment is severely lacking from the Esplanade.